micaschist

Micaschist is a metamorphic rock within the schist family that is characterized by a strong foliation and a dominant content of platy mica minerals, typically muscovite and/or biotite. The rock has a schistose texture with conspicuous, parallel mica crystals and commonly contains quartz and feldspar, along with accessory minerals such as garnet, zircon, and sometimes staurolite or kyanite.

Formation and conditions: Micaschists form during regional metamorphism of pelitic rocks, such as shales and mudstones, under medium to high temperatures and pressures. The mica-rich foliation develops as stress aligns the platy minerals, producing the characteristic schistose fabric. Mineral assemblages can vary with metamorphic grade; higher-grade varieties may host garnet, staurolite, kyanite, or sillimanite.

Texture and identification: The defining feature is the visible mica flakes arranged in parallel planes, giving the rock a sparkling, layered appearance. Color is influenced by the mica content and other minerals: muscovite-rich micaschists are lighter in color, while biotite-rich varieties appear darker. Accessory minerals such as quartz, feldspar, garnet, and sometimes cordierite or sillimanite may occur, aiding in sub-division by metamorphic grade.

Occurrence and context: Micaschist is widely found in mountainous and tectonically complex regions where regional metamorphism has affected pelitic terranes. It commonly lies between phyllite (lower grade) and higher-grade rocks such as gneiss in metamorphic sequences. Global examples occur in major orogenic belts including parts of the Appalachians, the Scandinavian Caledonides, and similar terrains.